Lithospheric structure and geologic development of a collisional orogen: Insights from the central Alaska Range

Patrick R. K Brennan, Purdue University

Abstract

The long-term distribution, mode, and progression of deformation along a collisional boundary are all fundamental, though poorly understood, processes of convergent margins. The investigation of these processes requires observations throughout the lithosphere and the integration of geophysical and geological datasets. The central Alaska Range is an ideal location to study these processes due to the well-exposed surface geology, and recent high-resolution geophysical surveys. Analysis of two receiver function transects across the Mesozoic Alaska Range orogen document three distinct crustal sections based on observations of crustal thickness, intra-crustal discontinuities and Vp/Vs. We interpret these sections and their geophysical attributes to correspond with the former continental margin, the suture zone proper, and the allochthonous oceanic terrane of the orogen, respectively. The observed variability in the crust across the central Alaska Range is likely controlled by the different lithologic composition of each of the terranes, and controls how each section responds to convergent margin stresses. By combining geologic data with receiver function observations, we have developed an integrated lithospheric-scale cross-section from the upper mantle to the surface for the Alaska Range orogen. Our cross-section delineates three major sections with distinct geologic histories that are separated by lithospheric-scale boundaries with distinct Moho offsets. The long-term geologic development of the Alaska Range orogen documents the progression from a distributed deformational mode to a more localized mode as the orogen evolves. To better understand the Neogene timing of exhumation of the central Alaska Range we have analyzed six, stratigraphically controlled, detrital zircon samples from Miocene – Pliocene sandstone of the Tanana foreland basin. Lower Miocene strata from the Tanana basin have detrital zircon ages with dominant Precambrian populations that are attributed to source areas north of the Alaska Range. During the Early – Middle Miocene the provenance of the Tanana basin switches to a distinctly Mesozoic source signal attributed to source areas within and south of the Alaska Range. The Early – Middle Miocene change in provenance is interpreted to represent the onset of Neogene uplift of the central Alaska Range.

Degree

Ph.D.

Advisors

Gilbert, Purdue University.

Subject Area

Geology|Geophysics|Geophysical engineering

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